I recently purchased a brand-new Ostro VAM frameset - a demo bike built with Shimano for display purposes. I bought just the frameset, migrated some SRAM parts (RED crankset and rear cassette), and had my LBS install new Force shifters and derailleurs. Since the build, I’ve had nothing but issues.
Timeline:
First 14 days: Derailleur hanger keeps coming loose. LBS tightens it.
Next 2 months: Frequent chain drops (falling behind the small chainring and wedging between the frame and ring), plus chain skipping/slipping on the rear cogs under load. I make micro-adjustments using the SRAM AXS app.
Bike trip - Day 1: Same issues resurface. A local bike shop discovers the derailleur hanger is loose again. Pay $60 for a drivetrain tune-up.
Bike trip - Day 2: Creaking sounds from the bottom bracket.
Post-trip: Return to the original LBS. They discover a crack in the joint between the crank arm and spindle (apparently a known issue with this crankset). Get it warranty replaced. LBS tweaks the drivetrain and fixes the threads, and shifting is now smooth and quiet.
Current issues: Chain dropped again (shifting from the large to the small chainring while in the middle of the cassette). During sprint practice, the chain keeps skipping down to the smallest cogs under power.
I’m fed up and confused. Is this something to do with my riding, or does the drivetrain have fundamental issues? Does anyone have insight into what might be going on?
I’d say it’s reasonable to expect that none of those things would be a regular issue. Chain drops can have a number of causes. Alignment issues, compatibility issues, drivetrain fine-tuning issues or just general drivetrain wear. A bike shop shouldn’t have any issues diagnosing and resolving any of these however.
If you’re willing to let us know where you’re based there may be some alternative bike shop suggestions. It’s difficult to say your LBS is doing a good or bad job but it sounds like they’re struggling to resolve the issue.
Isn’t the mech hanger on this bike mostly held in by the thru axle? The little machine screw is largely just to stop the hanger from falling out when you remove the wheel.
So if the hanger is loose with the wheel in and thru axle appropriately tight something odd is happening.
I’ve had issues on some frames with the carbon mating surface not being flat which stops the hanger from sitting straight. This has caused creaking sounds as well. I wouldn’t say this issue has caused unwanted shifting under load though.
Unwanted shifting under load would suggest something is moving or bending under load. Hopefully not the frame.
The unwanted shifting and loose hanger could be the same problem.
I think you are on the right track here. My Scott Sportster Gravel uses that method to secure the hanger - and the screw loosens over time despite several attempts to Loctite it in firmly. This causes the rear derailleur to be misaligned if I remove and refit the rear wheel. It happens intermittently, so much so that I get the kind of issues the OP faces (dropped chain and poor shifting) seemingly randomly and scratch my head over it - until I remember to check the hanger. Now I ensure I pull the hanger to the rear and upwards with my fingers whenever I insert the wheel and keep it in place while tightening the skewer. Gives me the shits…
Yep, that makes sense to me too. 12 speed stuff has pretty tight tolerances for chain alignment, so having a slightly loose derailleur hanger would almost certainly affect shifting and cause chain skips. I can easily imagine doing minor shifting tweaks that work for a ride or two and then everything goes back out of alignment, seemingly randomly. Also checks out that issues pop up right after you’ve traveled with the bike (and likely removed the rear wheel). Combine a loosey-goosey derailleur hanger with a cracked crank…..multiple parts of the drivetrain are moving around when they shouldn’t; no surprise at all that you’re having issues.
Sounds like the crank issue has been solved, so next I would look at the derailleur hanger/frame interface. Might be able to slightly modify one or the other for a better fit, might be a common issue with that frame that has a known solution, might end up being a warranty issue. I would also check the thru axle, if that’s what’s mostly holding the derailleur hanger in place.
Whatever the solution, your riding is definitely not the problem!
Sounds like a stern conversation with the owner needs to be had. I had this happen to me, it nearly caused me to crash the second time. I spoke to the owner and read him the riot act. Sometimes politeness ha to be backed up with firmness where required.
